Tectonic, Volcanic, and Geothermal Comparison of the Tohoku Volcanic Arc (Japan) and the Cascade Volcanic Arc (USA)

Abstract

Both the Tohoku volcanic arc of N Honshu and SW Hokkaido, Japan, and the Cascade volcanic arc of NW United States and SW Canada are related to subduction of an oceanic plate beneath a continental plate. The Tohoku arc, however, displays much greater volcanic and geothermal activity than the Cascade arc. A cooperative project between the Geological Survey of Japan and the U.S. Geological Survey seeks to document the factors responsible for these differences and to quantify the implications for geothermal resource assessment. Large modern geophysical and geological data sets for both arcs are being compiled digitally at Preliminary analysis suggests that the greater volcanic and hydrothermal vigor of the Tohoku arc may be due to enhanced hydration of mantle peridotite and consequent greater magma generation. in turn caused by the greater age and hydration of the Pacific Plate and the faster rate of its subduction as compared to the Juan de Fuca plate under the Cascade arc. In addition, more extensive mechanical interaction between the Pacific plate and the mantle wedge beneath the Tohoku arc may promote increased convection in the mantle wedge and consequent greater generation of magma than in the mantle wedge beneath the Cascade arc.